4 Answers
4

Yes. And you should be able to see that because the format box will automatically be checked. If you want to enable the two main features of ext4 that can be added without reformatting, run sudo tune2fs -O extents,uninit_bg /dev/sda1 and then sudo e2fsck -f /dev/sda1.

Where do you want to change it? As far as I can imagine, if you install new version of ubuntu, any selection about a new file system means destroying the previous. Since you mentioned "my home" (I am not sure you mean that /home is mounted as a separated filesystem), if I were you, I would simply skip using that fs, and later, you only need to edit /etc/fstab to mount your "old" /home. Note: if you choose ext4 fs there (but /home was ext3) this means some kind of "conversion" from ext3 to ext4 then (ext3 can be mounted az ext4, but if you do this even only at once, you can't "revert" it easily ...).

Ah, you're right, I forgot to mention in my answer that just mounting an ext3 as ext4 does not enable all fancy new functionality of ext4, some tune2fs can be useful to enable those too ...
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LGBFeb 14 '11 at 6:42